<?php
class Permissions
{
    public static function permStringToInt($PermString)
    {
        $strings = str_split($PermString);
        if (count($strings) == 9) {
            $chunks = array_chunk($strings, 3);

            $return_text = "";
            foreach ($chunks as $groups) {
                $group_number = 0;
                foreach ($groups as $permission) {
                    if (in_array($permission, array('r', 'w', 'x', '-'))) {
                        if ($permission == 'r') {
                            $group_number+=4;
                        } else if ($permission == 'w') {
                            $group_number+=2;
                        } else if ($permission == 'x') {
                            $group_number+=1;
                        }
                    } else {
                        return "Invalid string!";
                    }
                }

                if ($group_number <= 7) {
                    $return_text .= $group_number;
                } else {
                    return "Invalid string!";
                }
            }
        } else {
            return "Invalid string length!";
        }

        return $return_text;
        //throw new Exception('Not implemented');
    }
}

// For test purposes only
// echo Permissions::permStringToInt("rwxr-x-w-");
echo Permissions::permStringToInt("rwxrwx---");
// Should yield 752